Senior security sources quoted by the Sunday Times said the unnamed rebel spy is fighting to give evidence to a forthcoming Intelligence and Security Committee (ISC) inquiry into torture.
The retired individual is said to have had access to the very highest levels of intelligence and is thought be willing to give evidence on a series of key, top level briefings held within MI5 at the outset of the war on terror.
The meetings were held when Baroness Eliza Manningham-Buller took over Britain’s internal security agency from Stephen Lander in 2002.
The ex-spy is expected to say trained CIA interrogators carried out torture and that British agents were present when Guantanamo detainees were hooded, chained, waterboarded and subjected to psychological abuse.
The ISC has set no date on the inquiry, but told the Times the investigation would be a “substantial inquiry into the role of the UK government and security and intelligence agencies in relation to detainee treatment and rendition.”
MI5 has always said it neither tortures nor condones the use of torture, but questions remain over its knowledge of the practice in the post 9/11 wars.
British resident Shaker Aamer was released from Guantanamo in October 2015 after 14 years in detention. He maintains he was tortured during his captivity with British officials present.
The south Londoner claims that during one incident he was slammed against a wall while a British officer was in the room, while on another occasion a British soldier visited him while he was held in a cage.
The allegations even appear to have caused considerable concern within the security services.
“There was a great deal of discomfort within MI5 around the 2002 period that the agency was receiving intelligence obtained via either torture or severe abuse,” one intelligence source told the Sunday Times.
“The view among many officers, although it was by no mean unanimous, was that Britain should have nothing to do with intelligence obtained by torture or abuse — call it what you will.”